It is known that when running over the ground, for example over an accessway or a runway of an airport, the steering of an aircraft is performed by way of the deflection of the nose landing gear. In order for a pilot to be able to carry out such steering over the ground under the best possible conditions, it is of course necessary that, in the undeflected position, the nose landing gear be parallel to the fuselage of the aircraft so that a rightward (or leftward) deflection command causes a proportional deflection of the wheels to the right (or to the left) and that with no deflection, the aircraft runs straight ahead.
The orientation of the nose landing gear is generally adjusted at the stage of manufacture of said gear. However, despite the existence of such initial adjustment, it may happen that subsequently the wheels of the nose landing gear are no longer oriented entirely parallel to the fuselage so that the pilot must then compensate for a drift of the aircraft to one side when he wishes to run straight ahead, for example in the center of a runway. Such a maladjustment must of course be corrected, in particular for reasons of comfort of ground running, as well as for safety reasons.
However, to be able to correct such a maladjustment, it is necessary to know the exact orientation of said nose landing gear with respect to the longitudinal axis of the aircraft.